1. Field of the Invention
The present invention relates to an image processing apparatus, an image forming apparatus, an image processing method, and a computer-readable storage medium.
2. Description of the Related Art
Conventionally, among image forming apparatuses such as a printer, a copying machine, and a multifunction peripherals (MFP), for example, in an electrophotographic image forming apparatus, an image carrier such as a photosensitive element is deteriorated, resulting in image deterioration due to transfer nonuniformity on solid areas and characters in an image in some cases. In particular, in an image forming apparatus using a process cartridge in which a photosensitive element (image carrier) and a developing unit that houses toner (image forming material) are integrated with each other, if an amount of remaining toner becomes smaller and is closer to a so-called toner-near-end, transfer nonuniformity of a single color of black (K) occurs significantly. If image nonuniformity such as the transfer nonuniformity occurs, as illustrated in FIG. 10, a print density is lowered and an image, in particular, characters become pale, resulting in deterioration of image quality.
Then, conventionally, as illustrated in FIG. 11, a black solid area is formed in such a manner that four colors of cyan (C), magenta (M), yellow (Y), and K overlap. This prevents deterioration of image quality or the like due to image nonuniformity such as transfer nonuniformity from occurring.
However, in the conventional method of preventing image nonuniformity such as transfer nonuniformity by printing with four colors of CMYK, an image area, such as text and graphics, which is printed with a single color of K in a normal state, is printed with the four colors of CMYK. Therefore, a large amount of toner is consumed and color deviation occurs in printing with the colors to be used for printing, resulting in deterioration of image quality.
Japanese Patent Application Laid-open No. 2009-190347 discloses as follows. Image data is analyzed, and a character area formed by a character having a saturation of equal to or smaller than a predetermined value is extracted. Then, the character area is separated into a contour portion of the character and an internal portion of the character. Furthermore, the image data of the character contour portion and the image data of the character internal portion are converted into ink amount data for at least one type of achromatic ink and at least three types of chromatic inks. In this case, the image data of each portion is converted to the ink amount data such that the chromatic inks are used in the character internal portion more than in the character contour portion. With this method, a clear character with less blurring is formed.
However, in the conventional technique as described in Japanese Patent Application Laid-open No. 2009-190347, a character is printed not only with the color of K but also with the colors of CMYK. Therefore, there is a problem that color deviation is easy to occur among the colors of CMYK, resulting in deterioration of image quality.
Therefore, there is a need for an image processing apparatus, an image forming apparatus, an image processing method, and a computer-readable storage medium that can suppress transfer nonuniformity and color deviation so as to improve image quality while reducing the consumption of an image forming material.